In the application of coatings, particularly liquid coatings, to circuit boards, efforts have been made in the prior art to achieve a more efficient coating apparatus and to provide a faster method of application of the coating material. Where application of a coating to the surfaces of both sides of two sided circuit boards is required, however, the optimization of the apparatus and of the method of applying the coatings to the two opposite surfaces of circuit boards have not been optimal.
One method and apparatus of the prior art is illustrated and described in U.S. Pat. No. 4,867,099, which discloses a coating apparatus having one applicator gun positioned beneath the circuit board to coat the bottom surface of the board at one coating station and a second applicator gun positioned above the board to coat the top surface of the board at a subsequent coating station to which the board is routed after being coated at the first coating station. With such an apparatus, circuit boards are continuously conveyed in a single direction sequentially through the two coating stations at which the two opposite sides of the circuit board are sequentially coated and then conveyed to an oven where the coating is dried. To convey the boards through this apparatus, the boards are loaded onto a conveyor upstream of the first coating station and removed from the conveyor downstream of the oven while being maintained in the same orientation as they are being conveyed through the two coating stations. With many circuit board coating materials, however, application of the coatings from below is less desirable, and less effective and efficient, than where such coatings, particularly liquid coatings, are applied from above.
Another approach taken by the prior art is set forth in U.S. Pat. No. 4,900,580, which also discloses a system having two coating stations spaced along a conveyor. With this approach, an applicator gun positioned overhead in each coating station and the circuit boards are loaded onto the conveyor upstream of the first coating station. The circuit boards are then conveyed through the first coating station where coating material is applied downwardly from above upon the upwardly facing surface of each board. Each circuit board, with one of its surfaces coated and facing upwardly, is then conveyed to an inversion station located between the two coating stations at which the board is inverted to bring its formerly downwardly facing uncoated surface into an upwardly facing orientation so that it too may also be coated from above at the second coating station. By inverting the circuit boards between the two coating stations, the necessity of applying a coating material to the circuit board from below, sometimes undesirable, is avoided.
Another approach taken by the prior art is disclosed in U.S. Pat. No. 4,871,584. In this approach, the necessity of providing two coating stations is eliminated by a method of conveying a circuit board through a single coating station in one direction where the upwardly facing side is coated, then inverting the board and conveying it back through the same coating station in the reverse direction to coat the upwardly facing surface on the opposite side of the board. This too eliminates the necessity of coating the board from below and does so with only one coating station. A disadvantage of this approach is that the single coating station provided is idle during the time it takes each board to be removed from the coating station after the first side has been coated, inverted, and returned to the coating station for the coating of the second side. This sacrifices production efficiency to save one coating station and one coating dispensing device.
Accordingly, there is a need to provide a method and apparatus that requires only a single coating station, allows that coating station to apply coating material, particularly a liquid coating material, to circuit boards from only one side thereof, preferably from above, and which coats both sides of the printed circuit board without leaving the coating station idle during the time it takes to invert the circuit board to bring its opposite side to an orientation which faces upwardly to receive the material applied from the overhead coating device.